The present invention pertains to radio-frequency welding, and more particularly, to an apparatus and methods for radio-frequency welding flexible materials.
It is often desirable to join together flexible thermoplastic materials, such as vinyl sheeting or coated fabrics, without stitching that would create holes in the materials through which liquid could penetrate. A common method for forming such a joint is by welding two or more flexible materials together using radio-frequency (R-F) welding, also known as high-frequency welding. R-F welding fuses materials together to form an integral weld, thereby eliminating the need to stitch the materials together. Thus, R-F welded joints are particularly useful in the manufacture of articles such as hospital mattress covers, as described in U.S. Pat. No. 5,910,081 to Graham, where the prevention of liquid penetration is critical for health and safety reasons.
Prior methods of forming R-F welds in flexible materials have involved the use of bar presses, where a single, elongated electrode bar is attached to a moveable upper or lower platen of the press. An operator typically positions the materials desired to be joined on a lower platen of the press, usually registering the material in a jig to ensure proper alignment of the weld with respect to the materials. Once the materials are in position, the upper platen and attached electrode bar are lowered so that the materials are compressed between the electrode bar and the bottom platen. Radio-frequency energy is applied to the electrode bar while the materials are being compressed in order to weld the materials together.
If the length of the desired weld joint is longer than the length of the electrode bar, the operator must raise the upper platen and reorient the workpiece to position an unwelded portion of the workpiece beneath the electrode bar. The press must be closed another time to weld the materials at the new location. In this manner, two or more successive workpiece-positioning and press-closing operations may be required to create long weld sections. These multiple, repeated operations result in manufacturing inefficiencies and long cycle times in the production a welded article.
Further manufacturing inefficiencies result from the fact that workpiece positioning operations must be performed while the press is open, and is thus inoperative and under-utilized. These inefficiencies and equipment underutilizations drive up manufacturing costs, making the manufacturer less competitive in the marketplace.
Accordingly, there is a need for an apparatus and methods for R-F welding flexible materials that provide decreased cycle times per workpiece and increased press utilization while continuing to provide quality indexed welds in properly aligned materials. Thus it is an object of the present invention to provide an apparatus for use with an R-F press that will reduce cycle times and increase press utilization.
It is a further object of the invention to provide methods of R-F welding that will reduce cycle times and increase press utilization.
The present invention provides an apparatus and methods which increase manufacturing efficiencies and utilization of press equipment in welding flexible materials. In accordance with one aspect of the present invention, an apparatus for use in a welding press includes a base with a work surface and an electrode independent of and not attached to a platen of the press. The base and electrode have corresponding electrode locating features and the electrode is used to directly register on a workpiece when the electrode is positioned on the base. Because the electrode of the present invention is used to locate and hold the workpiece, the invention provides an advantage over prior R-F presses by eliminating the need for extensive fixturing to locate and hold a workpiece relative to an electrode which is generally attached to a moving platen of the press. According to the invention, set-up operation can be conducted in an area spaced from the moving platen and not restricted by it.
In another aspect of the present invention, multiple electrodes may be used on a single base to create multiple welds in the same workpiece in each cycle, or alternatively, multiple welds in different workpieces in each cycle. The present invention thus provides increased throughput per press-closing operation, compared to conventional bar presses which generally have a single electrode and can only weld a single section during each press-closing operation.
In a further aspect of the present invention, a base is mounted to a shuttle that can be slidably moved beneath and out from under a press platen. The electrode is disposed on the base in a fixture on the shuttle. Thus, electrode to work piece indexing is provided outside the closed platen station. When two or more bases and shuttles are used in a single press, the present invention reduces press underutilization and increases manufacturing efficiency by allowing multiple operators to perform both welding and workpiece positioning operations simultaneously.
In another aspect of the invention, a method for R-F welding flexible materials includes the steps of orienting a workpiece on a fixture; placing an electrode on the fixture to register and hold the workpiece; moving the electrode, fixture, and workpiece into a welding press; applying pressure and energy to the electrode; removing the electrode, fixture, and workpiece from the press; and removing the workpiece from the fixture.
In yet another aspect of the invention, shuttles and bases are used with conventional bar presses to increase utilization of bar press equipment. Accordingly, another aspect of the present invention contemplates a method of using a shuttle with a conventional bar press, including the steps of orienting a workpiece on a work surface, using a shuttle to slide the workpiece beneath a platen and electrode of the press, closing the press and applying pressure and radio-frequency energy to the electrode, opening the press, sliding the shuttle out from under the platen, and removing the workpiece from the work surface.
These and other aspects of the invention will be apparent from the following description, claims, and attached drawings.